1. Field of the Invention
The present invention relates to a pump equipment having plural rotary pumps and a method for assembling the pump equipment. In particular, the present invention is preferably applied to an internal gear pump such as a trochoid pump or the like for brake apparatus for vehicles.
2. Description of Related Art
A rotary pump, for example, an internal gear pump, is comprised of a drive shaft to be driven by a motor, an inner rotor and an outer rotor to be rotated by the drive shaft and a casing for containing the drive shaft and the inner and outer rotors. The casing is provided with a pump room in which the inner and outer rotors are contained, an intake port and a discharge port for sucking and discharging oil and a shaft hole communicating to the pump room from the motor side. The drive shaft is fitted into the inner rotor through the shaft hole.
As an example of the pump in which two rotary pumps are rotated by a drive shaft, a tandem pump equipment is described in JP-A-H.9-126157. In the tandem pump equipment, the discharge ports of the two rotary pumps are provided, respectively, in the same direction from the drive shaft and the intake ports, respectively, in the same direction from the drive shaft, but in the opposite direction from the respective discharge ports. Each pressure at the respective discharge ports of the two rotary pumps is reacted in the same direction against the drive shaft and the drive shaft receives an unbalance force so that the pump operation may be adversely affected due to the bending of the shaft.
An object of the present invention is to provide a pump equipment having a plural of rotary pumps capable of smoothly rotating the pumps because of a limited bending of their drive shafts. The pump equipment has a construction that the respective discharge ports of the rotary pumps are located at the points which are nearly symmetrical with respect to the center axis of the drive shaft. The respective reaction forces against the drive shaft to be produced by the high pressure at the respective discharge ports may be counterbalanced each other so that the possible bending of the drive shaft may be limited.
As an another aspect of the present invention for limiting the bending of the drive shaft for the pump equipment having two rotary pumps, the intake and discharge fluid conduits of one pump and the intake and discharge fluid conduits of the other pump are arranged at the locations which are, not between the pumps, but outside from the pumps, respectively. Preferably, These locations of the intake and discharge fluid conduits will serve to narrow the space between the two pumps so that the pump equipment may become compact.
As a further aspect of the present invention, two bearings for holding the drive shaft are arranged outside the two pumps, that is, at the respective positions between which the two pumps are inserted. The forces due to the high pressure at the discharge ports are reacted against the drive shaft inside the two bearings. Therefor, the bending of the drive shaft is more limited, compared with a case that the forces are reacted against the drive shaft outside the two bearings.
Furthermore, it is one of the objects to provide a method for assembling the pump equipment in such a way that a part of the peripheral border between respective cylindrical members piled up for constituting the casing is tentatively welded by laser beam at first and, then, all around the peripheral borders are finally welded. Such a method is effective for limiting a deformation or a position shift of the respective members, because the energy of the tentative spot welding by laser beam is less than that of the final welding and, therefor, the deformation force by laser beam is not so strongly influenced.
It is preferable to apply to the welding portions the laser beams from plural side positions at the same time so as to counterbalance each other the respective forces given by laser beams to the welding portions. This method may be used in the above tentative spot welding. Furthermore, such a method makes it possible to weld all around the peripheral borders without causing the deformation or the position shift of the respective cylindrical members, even if the tentative spot welding is eliminated and the relatively large energy of laser beams is applied at the same time to the welding portions.
It is a final object of the present invention to provide a brake apparatus having a hydraulic circuit in which the pump equipment described above is applied. The pump equipment is used for increasing fluid pressure to wheel cylinders in the hydraulic circuit. In particular, each of plural rotary pumps is operative in each of fluid conduits separately provided in the hydraulic circuit.